Recent developments in magnetic topological insulators (MTI) such as antiferromagnetic MnBi₂Te₄ opened new arenas for electric control of magnetization dynamics. PI-Cheng’s group formulated the spin-orbit torque (SOT) arising from the topological electrons in antiferromagnetic MTI as well as its reciprocal effect—topological charge pumping. For undoped MnBi₂Te₄, the SOT originates from the adiabatic current of valence electrons, which does not incur Joule heating as ordinary current-induced torques. The proposed SOT acts oppositely on two neighboring magnetic layers, whereby an applied AC electric field can drive the resonance of the exchange mode with a frequency lying in the sub-THz regime. The SOT-induced exchange resonance manifests as a sharp peak in the effective optical conductivity, entailing a remarkably weaker energy dissipation compared to ordinary ferromagnetic and antiferromagnetic resonances driven by conventional SOT. In trilayer antiferromagnetic MnBi₂Te₄, a hitherto unknown exchange resonance lying in the sub-THz regime is predicted, which does not react to microwave radiations but can only be driven by the unconventional SOT in MTI. This works opens new pathways to manipulate MnBi₂Te₄ and similar antiferromagnetic MTIs by electrical means.

This theoretical work has been published in Physical Review B and is available here.